Inorganic-organic nanocomposites can exhibit mechanical properties superior to those of their separate components. To optimize the performance properties of these materials, it is usually desirable to disperse the inorganic components in the organic matrix on a nanometer length scale. Clays and other layered inorganic materials that can be broken down into nanoscale building blocks are useful for the preparation of inorganic-organic nanocomposites.
The addition of clay materials to polymers is known in the art, however, incorporating clays into polymers may not provide a desirable improvement in the physical properties, particularly mechanical properties, of the polymer. This may be due, for example, to the lack of affinity between the clay and the polymer at the interface, or the boundary, between the clay and polymer within the material. The affinity between the clay and the polymer may improve the physical properties of the resulting nanocomposite by allowing the clay material to uniformly disperse throughout the polymer. The relatively large surface area of the clay, if uniformly dispersed, may provide more interfaces between the clay and polymer, and may subsequently improve the physical properties, by reducing the mobility of the polymer chains at these interfaces. By contrast, a lack of affinity between the clay and polymer may adversely affect the strength and uniformity of the composition by having pockets of clay concentrated, rather than uniformly dispersed, throughout the polymer. Affinity between clays and polymers is related to the fact that clays, by nature, are generally hydrophillic whereas polymers are generally hydrophobic.
Clay minerals are typically comprised of hydrated aluminum silicates that are fine-grained and have a platy habit. The crystalline structure of a typical clay mineral is a multi-layered structure comprised of combinations of layers of SiO4 tetrahedra that are joined to layers of AlO(OH)2 octahedra. Clay minerals vary based upon the combination of their constituent layers and cations. Isomorphic substitution of the cations of clay mineral, such as Al3+ or Fe3+ substituting for the Si4+ ions in the tetrahedral network, or Al3+, Mg2+ or Fe2+ substituting for other cations in the octahedral network, typically occurs and may impart a net negative charge on the clay structure. Naturally occurring elements within the gallery of the clay, such as water molecules or sodium or potassium cations, are attracted to the surface of the clay layers due to this net negative charge.
In order to promote more affinity between the clay and the polymer at the interface and provide a uniform dispersion of the clay within the polymer, the interlayer surface chemistry of the clay may be modified to render the silicate layers less hydrophilic
Alkylammonium ions, such as onium salts, are commonly used to prepare clay dispersions for nanocomposite materials. The basic formula for a typical alkylammonium ion is CH3—(CH2)n—NH3+ where n is from 1 to 18. It is believed that the alkylammonium ions also readily exchange with the naturally occurring cations present between the clay platelets resulting in an intercalated state. Further, it is believed that the alkylammonium ions may increase the space between the clay layers and also may lower the surface energy of the clay thereby allowing organic species with different polarities to become intercalated between the clay layers.
A need exists for nanocomposites having improved properties. The invention disclosed herein provides a cost effective and efficient process for the production of novel inorganic-organic nanocomposite compositions that are is especially suitable for use in sealants with the desired characteristics of softness, processability and elasticity are important performance criteria.